In general, a magnetic recording medium comprising a non-magnetic support having formed thereon a magnetic layer composed of ferromagnetic particles dispersed in a binder is used as magnetic recording media such as audio tapes, video tapes, computer tapes, etc.
In response to the recent demand for high density recording in magnetic recording media, it has been practiced to reduce the particle sizes of ferromagnetic fine particles, improve the dispersibility of ferromagnetic fine particles, improve the surface property of a magnetic layer, and improve the packing density of ferromagnetic fine particles.
For example, in order to improve the dispersibility of ferromagnetic fine particles, dispersing agents are used for preparing magnetic coating positions, and also it is recently proposed to improve the dispersibility of ferromagnetic fine particles by using a polyurethane resin containing a metal sulfonate and a vinyl chloride resin as a binder, namely by introducing polar groups into the binder, as described in JP-A-61-123017 (the term "JP-A" as used herein means as "unexamined published Japanese patent application").
Also, it is known to improve the surface property of the magnetic layer by increasing the temperature or pressure for a calendar treatment of a magnetic recording medium, and also improve the surface property of a magnetic recording medium by grinding the surface of the magnetic layer by a grinding tool, as described in JP-A-63-98834.
Furthermore, it is proposed to polish the surface of the magnetic layer by a polishing tape for providing a magnetic recording medium causing less clogging of a magnetic head and less occurrence of dropout in JP-A-63-259830.
It has been found that by the aforesaid improvements, the number of readily releasable particle components such as ferromagnetic particles from the surface of the magnetic layer is reduced to greatly decrease the occurrence of dropout and clogging of a magnetic head.
However, although the occurrence of dropout and clogging of magnetic head is reduced, fast sticking on magnetic head (i.e., components of a magnetic layer are locally fast-stuck on the surface of a video head during running of a magnetic recording tape to reduce the output) occurs and the phenomenon is particularly severe when the crystallite sizes of ferromagnetic fine particles are from 350 to 500 angstrom.
That is, a magnetic recording medium having improved electromagnetic conversion characteristics for high density recording generally tends to reduce the running property and durability thereof. In particular, the occurrence of the fast sticking phenomenon on magnetic head tends to become severe in a magnetic recording medium for high density recording.
In other words, it has been found that even by employing the aforesaid improving methods, a magnetic recording medium having improved running characteristics without causing fast sticking on magnetic head can not be obtained.